fix(dataset): avoid crash if database missing

[villebro]

SUMMARY

When a dataset is referencing a database that is no longer present, trying to edit the dataset fails:

After the fix, it's possible to change edit the dataset as expected:

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[kgabryje]

LGTM!

[codecov]

Codecov Report

Merging #19582 (0cfdd8e) into master (e1ef2ba) will increase coverage by 0.06%.
The diff coverage is 54.34%.

❗ Current head 0cfdd8e differs from pull request most recent head a32b27b. Consider uploading reports for the commit a32b27b to get more accurate results

@@            Coverage Diff             @@
##           master   #19582      +/-   ##
==========================================
+ Coverage   66.59%   66.65%   +0.06%     
==========================================
  Files        1682     1680       -2     
  Lines       64321    64280      -41     
  Branches     6561     6564       +3     
==========================================
+ Hits        42837    42849      +12     
+ Misses      19783    19729      -54     
- Partials     1701     1702       +1     

Flag	Coverage Δ
javascript	51.46% <37.03%> (+0.09%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...et-ui-chart-controls/src/shared-controls/index.tsx	36.19% <ø> (ø)
.../legacy-plugin-chart-country-map/src/CountryMap.js	0.00% <ø> (ø)
...y-plugin-chart-country-map/src/ReactCountryMap.jsx	0.00% <0.00%> (ø)
...y-plugin-chart-sankey-loop/src/ReactSankeyLoop.jsx	0.00% <0.00%> (ø)
.../legacy-plugin-chart-sankey-loop/src/SankeyLoop.js	0.00% <ø> (ø)
...-chart-deckgl/src/layers/Screengrid/Screengrid.jsx	0.00% <ø> (ø)
...lugin-chart-echarts/src/BigNumber/BigNumberViz.tsx	0.00% <0.00%> (ø)
...src/BigNumber/BigNumberWithTrendline/buildQuery.ts	0.00% <0.00%> (-11.12%)	⬇️
.../BigNumber/BigNumberWithTrendline/controlPanel.tsx	33.33% <ø> (ø)
superset-frontend/src/SqlLab/actions/sqlLab.js	60.39% <0.00%> (-0.35%)	⬇️
... and 11 more

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